1. Field of the Invention
The present invention relates to a piezoelectric ceramic composition and a piezoelectric element using the piezoelectric ceramic composition.
2. Description of the Related Art
Conventional piezoelectric ceramic composition containing a lead titanate (PbTiO.sub.3) are known. Since a piezoelectric ceramic composition containing a lead titanate has a low dielectric constant and small particle size, it is suitable for the use in the high frequency range. Moreover, it has excellent characteristics such as ability in restraining sub-resonance due to large piezoelectric anisotropy, durability in use at a high temperature due to a high Curie point, and the like. Therefore, use of a piezoelectric ceramic containing lead titanate is indicated in the field of filters, vibrators, or the like, intended to be used in a high frequency range. However, the piezoelectric ceramic containing a lead titanate has disadvantages such as difficulty in obtaining a dense sintered compact having a large mechanical strength due to difficulty in sintering, and difficulty in polarization. In order to solve these problems, for example, a piezoelectric ceramic composition containing a lead titanate obtained by partially substituting the Pb of PbTiO.sub.3 by La and adding a Mn compound such as MnCO.sub.3 or the like has been used. Such piezoelectric ceramic has characteristics such as a good sintering property and capability of a polarization treatment at a high temperature in a high electric field. However, a problem is involved in that the piezoelectric ceramic has a poor temperature coefficient of the resonance frequency and thus when it is used in a filter or a vibrator, the passing frequency or the oscillating frequency changes drastically according to temperature. Therefore, it has been difficult to use a ceramic containing lead titanate in a filter or a vibrator, which are required to have a high accuracy.